Field of the Invention
The present invention relates to the field of enzyme engineering. It particularly relates to methods for deinking wastepaper by combined use of cutinase and chemical reagents.
Description of the Related Art
Secondary fiber, also known as renewable fiber, has been used in paper and paperboard production for many years. With the increasing demand of paper and paperboard over the world, and the rising awareness of environmental conservation, the protection of forest resources has been enhanced in countries around the world, leading to increased proportion of the secondary fibers usage in papermaking industry. Paper recovery and recycling is an effective way to solve the problems such as resource shortage, energy shortage and environmental pollution in the paper industry. It is also an important measure to implement cleaner industrial production and promote sustainable development. According to the survey of China Paper Association, the proportion of the secondary fibers in papermaking materials has been increasing year by year. The pulp consumption of China was 84,610 thousand tons in 2010. The consumption of wastepaper pulp was 53,050 thousand tons, which accounted for 63% of the total consumption, with a growth of 6.16% over the previous year.
Wastepaper deinking is generally the first process in renewable fiber recycling, which includes both chemical and physical reactions. Deinking reagents are usually used to destroy the adsorption between fibers and printing ink, and the ink particles are removed from fibers under a certain temperature and shear forces. The ink is mainly composed of pigment, connection material, and auxiliary reagents. The connection material is prepared by dissolving a small amount of natural resin, synthetic resin, rubber and other rubber derivatives in drying oil or other solvent. The protective effect of connection material on pigments makes it difficult to fall off from the fiber. Due to the stickiness of connection material, the pigment is difficult to be removed in deinking process, which affects the production of recycling pulp.
The traditional chemical flotation and washing method are still the main methods for wastepaper deinking in China. Washing method is carried out by washing pulp repeatedly with large amounts of water, which separates ink particles from fibers. It removes fillers and the fine fibers in wastepaper, which helps to achieve the purpose of cleaning. The flotation method is employed by attaching ink particles to bubbles so that ink particles can be removed by floating upwards with the bubbles. Conventional chemical methods have many shortcomings, such as requirement of large amount of alkaline substances, causing environmental pollution due to discharged waste water, requirement of large amounts of chemicals for waste water treatment and limited improvement of paper whiteness. Enzymatic deinking technology is the focus of researches in recent years. Many researches showed that it is efficient in improving flotation efficiency, reducing fiber loss, and reducing the amount of chemical usage. However, the current enzymatic method requires large amounts of enzyme, which limits its wide application due to the high cost. There is a need in developing a cost efficient enzymatic method for wastepaper deinking. The present invention satisfies this need and provides other benefits as well.